/ Central Valley Content for ºÙºÙÊÓƵ en /news/smog-forming-soils <p>A previously unrecognized source of nitrogen oxide is contributing up to about 40 percent of the NOx emissions in California, according to a study led by the University of California, Davis. The study traces the emissions to fertilized soils in the Central Valley region.</p> January 31, 2018 - 12:26pm Katherine E Kerlin /news/smog-forming-soils